1. Field of the Invention
The present invention is generally directed to an imaging device for use with an optical scope and, more particularly, to an imaging device configured such that an image generated by the device aligns with and overlays a scene image from the scope.
2. Description of Related Art
Military rifle operators are well trained in the use of direct view optical (DVO) scopes attached to the top of their guns. The DVO provides optical magnification as well projected reticles that help the operator determine the target range and firing solution. Because of the criticality of the alignment of the DVO to the gun barrel, military operators are often unwilling to remove the DVO in order to exchange it for a different type of scope technology, such as a thermal night vision imager.
Instead, devices known as clip-on imager devices are available that attach in front of the existing DVO scope to provide alternative scope technologies. The clip-on device includes a focal plane array (FPA) detector, such as a thermal imager or night vision intensifier, and objective optics to focus the scene (i.e. the vision field) onto the FPA detector. The detector may operate in any of a variety of spectral regions, including near-infrared (0.6-1.0 microns), short-wave infrared (1.0-2.5 microns), or thermal infrared (3-5 or 8-12 microns). Generally, the clip-on imager has a unity 1× total magnification so that it can be attached and removed from the host scope platform without changing the boresight relationships. The clip-on sensor is typically also designed to provide a field of view comparable to that of the original DVO scope. The clip-on imager also includes a display device and optics to collimate the display to the DVO scope.
An exemplary clip-on imager assembly, as is known in the prior art, is depicted in FIG. 1. As shown in FIG. 1, the clip-on imager device 10 is connected to a rifle barrel 12, and aligned with the DVO scope 14. The imager device 10 includes an FPA detector 16 and display device 18. The imager 10 further includes objective optics 26 for focusing an image onto the FPA detector 16 and projector optics 28 for collimating the displayed image back to the scope 14. In assemblies such as the assembly of FIG. 1, the DVO scope 14 effectively becomes part of the eyepiece for the entire assembly. In this case, the “normal” image of the DVO scope is no longer visible to the operator, as it is replaced by the image provided by the FPA detector 16. Clip-on imaging devices arranged as depicted in FIG. 1, are disclosed, for example, in U.S. Pat. No. 7,359,114 and U.S. Pat. No. 7,541,581.
The disadvantage of the current state of the art is that the clip-on device obscures the normal function of the DVO scope. Thus, the operator is made entirely dependent on the display projection and can no longer see the scenery directly. Therefore, an apparatus and method for aligning and overlaying the normal imagery of the DVO scope with the image obtained by the FPA detector of the clip-on device is needed. In this case, the user is able to “see” imagery from both sources at the same time. The device and assembly of the present invention are configured to provide such benefits.